Field of the Invention
The present invention relates to a cooling box.
Description of the Related Art
A cooling box includes a refrigeration device, and is configured to cool an item to be refrigerated at a fixed temperature through an evaporator configuring the refrigeration device disposed in a thermally insulated casing by intermittently operating the refrigeration device.
When an evaporator is disposed in the thermally insulated casing as such, frost is likely to be attached to the surface of the evaporator. Since this frost disturbs heat exchange between air in the thermally insulated casing and refrigerant in the evaporator, thereby reducing the temperature of the refrigerant, resulting in that the refrigeration device becomes unable to perform efficient cooling in the thermally insulated casing.
Thus, a cooling box is disclosed that is provided with a heater configured to prevent attachment of frost onto the surface of the evaporator disposed in the thermally insulated casing and to melt frost attached to the surface (see Japanese Patent Application Laid-Open Publication No. 6-159890, for example). For example, such a cycle is continuously repeated that the heater is operated while the refrigeration device configured to intermittently operate stops operating, thereby preventing attachment of frost onto the surface of the evaporator or removing frost attached to the surface while cooling the item to be refrigerated at a fixed temperature.
However, a method of continuously repeating the operation of the heater and the refrigeration device as described above result in the problem that energy efficiency is poor due to constant supply of the power to the electrical heater, the compressor, or the like for example.
Further, in the case where the operations of the heater and the refrigeration device are repeated uniformly, when the ambient temperature of the thermally insulated casing changes, the temperature inside the casing is affected by such change, resulting in the problem that it is difficult to maintain the temperature inside the thermally insulated casing at a fixed value. In this type of the cooling box, items to be refrigerated which should not be frozen, particularly, blood, vaccines, and medical products, cannot be preserved.